A traditional knee-ankle-foot orthosis (KAFO) is used to increase the patient stability during the weight-bearing phase of walking. A traditional KAFO locks the knee in full extension, which provides stability. This locked posture results in patients' ability to ambulate with gait deviations that can lead to overuse injuries. A stance control orthosis (SCO) allows a user's knee to flex during a swing phase of a gait cycle, and prevents knee flexion for stability during the stance phase. By allowing the knee to bend during the swing phase, SCOs allow a more natural gait, which may reduce secondary complications from gait compensations and allow the user to walk with less effort.
In general, stance control orthoses are known. By way of example, U.S. Patent Application Publication No. 2003/0153854 to Fillauer teaches a gravity-actuated knee joint locking system for a Swing Phase Lock (SPL) orthosis. The Swing Phase Lock orthosis uses a simple internal pendulum mechanism mounted on a thigh link (the member that moves in unison with the user's thigh). As the thigh link moves, the pendulum swinging motion locks and unlocks a shank link (the member that moves in unison with the user's shank) relative to the thigh link. This allows for locking and unlocking of the knee joint for different phases of a walking cycle.
By way of another example, a stance control orthosis by Ottobock (FreeWalk) and a knee-ankle-foot orthosis by Becker (UTX) work based on a similar principle. That is, dorsiflexion of a foot at the end of a stance phase pulls on a controllable cable connected to a locking mechanism at a knee joint. This pulling action disengages the locking mechanism to enable swing. The locking mechanism is spring loaded and locks the knee when the knee is fully extended.
In another example, an orthosis by Ottobock (Sensor Walk) uses a wrap spring at a knee joint for locking and unlocking the knee. This orthosis includes two sets of sensors: one at the knee to measure a knee angle and another at a footplate to measure force between the foot and the floor. The orthosis further includes a wrap spring clutch replacing a lateral knee joint to provide braking capability to support the anatomic knee joint; a microprocessor-controlled release for the brake; electronic circuitry; and a battery pack carried in a waist pack. Sensors in the footplate disengage the wrap spring clutch and allow the knee to bend in the late stance phase, when weight has been transferred to the contralateral side and is ready for single-limb support. A knee sensor senses extension of the knee after toe off and sends a signal to the microprocessor putting the wrap spring clutch in its locked position.
A Horton Stance Control Orthosis taught by U.S. Pat. No. 6,635,024 includes a locking mechanism that locks and unlocks the knee with the help of a push rod. The push rod is placed between the heel and the knee. The push rod locks the knee at heel strike and unlocks the knee right at the end of stance phase. The device locks knee at any angle.
In view of the devices discussed above, there remains a need to provide a stance control orthosis which can be simply and economically constructed, and which assists a wearer during walking. There is also a need for an orthosis device which does not require sensors or an electrical power source to operate.